SEM Imaging and the Benefits of Using Low kV

In this interview, AZoM speaks to Vern Robertson, EPMA Product Manager at JEOL USA, about the benefits of using a low kV in SEM imaging.

Can you give a brief overview of your company and the types of products you produce?

JEOL is a world leader in the manufacturing of scientific equipment. At its core are scientific instruments including its more widely known: TEM & SEM, as well as NMR, Mass Spec, Scanning Auger, XPS, EPMA, FIBs, semiconductor equipment (mask and wafer), and sample prep equipment. JEOL Ltd. was founded in Japan in 1946 and employs roughly 3500 employees worldwide in 32 countries. In 2020 JEOL celebrated 54 years ofSEM生产，60年的EPMAS，64年的NMR，56年的质量规格，2019年，TEMS 70年。美国JEOL美国为美洲的所有客户提供服务并支持。

What is the difference between a good SEM image and a great SEM image?

A good image provides information that will answer the question. That is the reason that the image is taken. It also should have all of the data information that allows the client or end-user to interpret the image such as kV, probe current, magnification, detector and its position, and most importantly a scale bar.

使图像成为上述所有图像的原因是图像的正确条件。好的图像对此没有错，但没有回答您要回答的问题！出色图像的另一个质量是没有伪影（充电，边缘效果，污染，光束损坏，样本准备不良，亮度和对比度，信号差，信号与噪声比率差），并且在视觉上“构架”良好。

低KV带来SEM图像有什么优势？

Low kV minimizes the artifacts normally seen at higher kVs: charging, edge effect, contamination, and beam damage. Most importantly, it provides surface-sensitive imaging. Murphy’s Law says, 'If you can’t see it you can’t image or analyze it, and at high kV, just because you see it doesn’t mean that it is all you are analyzing.'

为什么低KV会导致对生物或聚合物样品的样品损害较小？

In the past, theoretical calculations said that there is more sample damage at low kV due to the smaller interaction volume. That has been shown not to be true.Low kV electrons通常以较低的速度行驶，并且比高kV具有较低的光束电流密度。因此，您将越来越少的能量电子放入样品中。这也可以防止样品中的热量积聚，从而可以融化聚合物并破坏一些生物样品。

Can low kV improve EDS and WDS spatial resolution? If so, how?

绝对没错！随着加速电压的线性降低，X射线的生成体积呈指数下降，因此，即使kV的少量降低也会产生空间分辨率的增加。有三个警告：1）在非常低的kV时，X射线线的数量减少2）低kV并不是改善空间分辨率的唯一方法。选择正确的过电压是钥匙（光束KV与X射线线的能量）。3）SEM的类型（w/ lab6/ feg）。当您到达低KV和远光灯电流以防止信号强度通过W或LAB6 SEM降低时，探针直径就会大于X射线生成体积，因此您可以达到无回报的点。

The solution to this is an FEG source. This provides low kV with a very high probe current and maintains a very, very, small probe diameter overcoming all but the limited number of X-ray lines you can analyze.

Why would using a low kV for SEM imaging get overlooked?

In the 'old days' SEMs didn’t have low kV imaging and analysis capabilities. Also, higher kVs produce more signal so it was easier to image. Many people who occasionally use an SEM don’t want to be bothered to change the settings of the SEM that they were trained on. (Typically, 15 kV, moderate beam current, medium OL aperture, medium working distance, etc.). Also, in the past, SEMs had significantly lower imaging resolution at lower kVs, so the user shied away from it. Today’s SEMs, even entry-level, can image and perform microanalysis at low kV without much effort. We just need to convince them that this is the right thing to do.

Which instruments are best for taking SEM images at a low kV?

WhileFEG SEMSare “the best” for low kV and ultra-low kV (<1 kV, down to 10 V) all currently manufactured SEMs are very capable of low kV imaging. (1-5 kV).

What’s next for JEOL?

JEOL will continue to push the envelope in developing microscopes, imaging and microanalysis detectors, and software that will make this technology available to every research scientist and technician that would benefit from analyzing their samples with an SEM and continue to provide sales, service, and applications support to all of our customers.

关于Vern Robertson

VERN在JEOL USA工作了34年，并于2016年被任命为EPMA/SA产品经理，并将继续担任SEM技术销售经理，提供内部和现场，技术产品支持和客户应用程序支持。VERN于1986年开始担任JEOL的高级SEM应用专家，于2004年被任命为国家实验室经理，2005年为FEG SEM产品经理。新罕布什尔大学地质学博士学位。他先前的工业经验包括在独立测试实验室中进行八年咨询，专门研究工业和环境问题解决，包括偏光光学显微镜在内的职责，以及原子发射和吸收光谱，具有EDS/ WDS和X射线衍射。Vern是MAS（微分析学会）理事会的公司联络员，已有十多年的历史。